1. Field of the Invention
In general, this invention pertains to pest control systems, and in particular, to the fumigation of bulk-packaged commodities held in large shipping containers.
2. Description of the Related Art
The storage and shipment of bulk quantities of certain packaged commodities, such as sacked potatoes, onions, and baled hay, alfalfa and other fodder crops, constitute a significant portion of this nation's interstate and international commerce.
An efficient vehicle for these purposes is the well-known shipping container, which is about 8' wide by 8' high, and either 20' or 40' in length. These containers are often adapted to ride "piggy-back" on a tractor-trailer truck or flatbed rail car and to be stacked compactly by means of a large crane one upon the other in the hold of a seagoing vessel for shipments abroad. The interior volume of the container is typically accessed by means of a hinged door, or pair of doors, at the container's end.
The large quantity of commodities which can be held in such containers, coupled with the extended periods of time often associated with their storage or transportation over long distances, commonly result in the production and proliferation therein of vermin, such as rodents and insects, which feed on or nest in the commodity, which can result in its spoilage or consumption. Accordingly, a problem commonly associated with the bulk storage and shipment of commodities in large shipping containers is that of controlling these pests, which is typically accomplished by fumigation of the commodities with a pesticide while in the container.
A popular type of fumigant that has been in use for many years for this purpose is a metallic phosphide, such as aluminum phosphide (e.g., brands such as FUMITOXIN, PHOSTOXIN, DETIA, and GASTOXIN), which decomposes in the presence of water vapor to form hydrogen phosphide, or phosphine, a toxic gas effective as a pesticide, leaving a generally harmless powdered residue. This fumigant, which is typically provided in solid form, such as tablets or pellets, is described in more detail in U.S. Pat. Nos. 2,826,486, 2,826,527, and 3,132,067.
In the case of grain commodities, such as corn, soybeans, wheat and the like, which are typically shipped in loose bulk, or unpackaged form, fumigation can be achieved by placement of gas-permeable holders containing measured amounts of the fumigant at appropriate locations within the volume of the commodity itself, which placement can be accomplished either before or after the commodity is loaded in the container, such as a silo or the hold of a vessel. A device for placement of an apertured pipe before the grain is loaded, and introduction of the fumigant into the pipe through the upper surface of the grain thereafter, is described in U.S. Pat. No. 4,059,048. A method and apparatus for introduction of gas-permeable sleeves at strategic depths within such bulk-stored grain commodities, either before or after they are loaded, and the introduction into them of the fumigant through the commodity's upper surface after its loading, are disclosed in U.S. Pat. Nos. 4,579,714 and 4,641,573.
These fumigation systems, although effective when used in the context of loose bulk grain commodities held in large containers in which access is available to the upper surface of the grain, have been found to be unsuitable for fumigating bulk-packaged commodities, such as baled hay, which is held in shipping containers of the type described above, for several reasons.
First, the loading of such commodities into the containers usually involves relatively extended periods during which multiple trips are made into the container by loading personnel using, e.g., forklifts or dollies. Placement of the fumigant into the container before loading occurs could thereby result in exposure of these loaders to the fumigating gas.
Second, the packaging of the commodity, whether baled, sacked, boxed or otherwise packaged, and the packing or arrangement of the packages within the container, interfere with the introduction of fumigant holders between the packages after the container is loaded. The only accessible space left within the container for this purpose is usually the narrow, horizontally-extending "headspace" between the top layer of the commodity and the ceiling of the container.
Finally, known systems which involve the introduction of the fumigant into its holders after the commodity is loaded rely upon a vertical placement of the fumigant holders and a gravity feed of the fumigant into them, which in turn, requires a general access to the upper surface of the commodity itself. This access is not available in covered shipping containers, which are loaded and unloaded through the doors at their ends, as described above.
For these reasons, a substantial need exists within the industry for a system for fumigating bulk-packaged commodities held within shipping containers, in a quick, safe, reliable, effective, and inexpensive manner. The present invention fulfills this need and has other advantages as well.